Explanation:
In 1979, one of NASA's
Voyager
spacecraft made a spectacular and unexpected
discovery. Io,
the innermost Galilean moon of Jupiter, was covered
with volcanoes and some of them were erupting! In all, Voyager 1 observed
nine volcanic eruptions during its encounter with the moon.
When Voyager 2 flew past four months
later it was able to confirm that at least six of them were still erupting.
This Voyager image of Ra Patera, a large shield volcano, shows colorful
flows up to about 200 miles long emanating from the
dark central volcanic vent.